Crystal structure analysis of Ca₄YFe₅O₁₃ by combining 1 MeV high-resolution electron microscopy with convergent-beam electron diffraction

By combining 1 MeV high-voltage-high-resolution electron microscopy with convergent-beam electron diffraction (CBED), the crystal structure of a perovskite-related compound, Ca₄YFe₅O₁₃, is determined. The crystal has orthorhombic symmetry with lattice parameters a = 5.46, b = 37.4 and c = 5.54 Å. The space group is determined to be centrosymmetric Pnma by selecting the point group from the CBED patterns. The structure images taken from two principle-axis directions, which are interpreted on the basis of the calculated images, reveal that the structure consists of a succession of the stacking of FeO₆ octahedra (O layer) and FeO₄ tetrahedra (T layer) and is represented by the stacking sequence of ...OTOOTOTOOTO... along the b axis repeated at intervals of 37.4 Å. It is shown that the Ca₄YFe₅O₁₃ crystal structure can be described in terms of unit-cell-level twinning of Ca₂Fe₂O₅.